As an example of a high pressure side heat exchanger, in a radiator disclosed in JP-A-2001-221580, the insides of header tanks, which are connected to longitudinal ends of tubes, are respectively divided into two tank spaces. The refrigerant reverses flow direction twice while flowing through the radiator from a refrigerant inlet to a refrigerant outlet. Thus, three broad paths of the refrigerant flow are formed when the radiator is viewed in broad perspective. The number of the path is obtained by adding one to the number of times that the refrigerant reverses flow in the radiator.
In general, when a flow area of a refrigerant passage is small, the velocity of flow of the refrigerant is high, so efficiency of heat transfer increases and compressive strength improves. Therefore, it is possible to reduce the heat exchanger in size and weight.
On the other hand, when the flow area is excessively small, pressure loss in the refrigerant passage increases, resulting in decrease in the flow rate. In this case, it is required to increase the numbers of the tubes defining the refrigerant passages and thereby to restrict the decrease in the flow rate. However, this results in the increase of the heat exchanger in size and weight.